1. Field of the Invention
The present invention relates to a developing paper for receiving dye from a thermal transfer sheet having a predetermined area heated according to an image information so as to form a dye image.
2. Description of the Prior Art
The thermal transfer recording method is widely used. That is, a predetermined area of a thermal transfer sheet is heated by a thermal head or laser according to an image information so that a dye is thermally melted or dispersed from the thermal transfer sheet onto a developing paper, so as to form an image on the developing paper. This thermal transfer sheet has an ink layer made from a predetermined concentration of dye, and the dye is transferred from this ink layer to the developing paper. Recently, a special attention is paid to a so-called sublimation type thermal transfer recording method using a thermally sublimating dye for forming a full color image of continuous gradation. For example, a thermal transfer sheet is heated in dots according to an image signal of a video image, so that an image is formed on a video developing paper.
The video developing paper includes a sheet-shaped substrate made from polypropylene on which a dye layer for receiving an image. This image receiving dye layer receives a dye portion transferred by heat from the thermal transfer sheet and holds the dye portion. The image receiving dye layer is made from a thermoplastic rest which is easily dyed such as polyester, polycarbonate, polyvinyl chloride, vinyl chloride copolymer such as vinyl chloride-vinyl acetate copolymer, polyurethane, polystyrene, AS resin, ABS resin, and the like.
The developing paper also contains a plasticizing agent added to improve the dye transfer sensitivity and light-proof characteristic.
However, in the aforementioned developing paper, the thermoplastic resin and the solid plasticizing agent used in the image receiving dye layer does not melt well into each other, and the solid plasticizing agent often precipitates on the surface of the image receiving dye layer. In such a case, precipitated portion has a high dye transfer capability, which results in an uneven concentration on the entire image. Moreover, in the aforementioned developing paper, if the image receiving dye layer contains a liquid plasticizing agent, it may ooze out due to heat or humidity.
Thus, the plasticizing improves the light-resistance of the developing paper, but causes the problems of concentration unevenness and oozing out.